54 y M presents to the ED with complaints of chest pain starting acutely 4 hours ago.  The EKG is as follows:

Posterior Mi

What’s the diagnosis? 

Posterior MI.  Which is suggested by the following findings in leads V1-3:

  • Horizontal ST depression
  • Tall, broad R waves (>30ms)
  • Upright T waves
  • Dominant R wave (R/S ratio > 1) in V2

On EKG, because the electrical activity from the posterior portion of the myocardium is recorded from the anterior side the standard injury pattern becomes inverted.  Q waves become R waves, ST elevation becomes ST depression, and terminal T waves become upright.  In this case you would order a posterior EKG and look for ST elevation >0.5mm in leads V7-9 to diagnose posterior MI.  In this case the posterior EKG would look something like this:

Posterior Mi 2

Interesting facts about posterior MI and why it is important to be vigilant:

  • Posterior infarction accompanies 15-20% of STEMIs – usually occurring in association with an inferior or lateral infarction.
  • Isolated posterior MI  occurs in about 3-11% of all MIs.
  • Posterior extension of an inferior or lateral infarct implies a much larger area of myocardial damage and increased risk of cardiac dysfunction and death.
  • Isolated posterior infarction is an indication for emergent coronary reperfusion, but the lack of obvious ST elevation often leads to missed diagnosis.